Field
Embodiments of the disclosure relate generally to supersonic inlets for aircraft jet engines and more particularly to a caret inlet capable of varying ramp angle as well as capture area.
Background
Engine inlets for supersonic aircraft have complex aerodynamic requirements based on Mach number and other flight conditions. Fixed inlet geometries typically have highest efficiency at one specific Mach number and flight condition. Operation at other speeds or flight conditions results in degradation of the aerodynamic performance or efficiency of the inlet. To allow flight at varying Mach number, mechanical systems to adjust the capture area and ramp geometry of the inlet may be employed to increase efficiency. An existing solution to a variable ramps and variable capture inlet is the F-15 Eagle produced by The Boeing Company. This inlet system is highly efficient and is recognized as an optimized inlet design. However, later-generation fighters require unique shaping where the inlet aperture edges are highly swept. In such aircraft a caret-type inlet system is employed. Examples of aircraft employing such inlets are the F-18E/F Super Hornet produced by The Boeing Company and the F-22 Raptor produced by Lockheed Martin. These inlets are fixed geometry inlets and were designed for optimized operation at a particular flight Mach number. At off-design Mach numbers, a fixed-geometry inlet system may not provide the best shaping to maximize pressure recovery. In addition, because the inlet capture area is fixed, the inlet tends to capture more mass flow than the engine needs at lower speed than at the inlet sizing condition. As a result, the excess airflow will have to be spilled or dumped through a bypass; both of which will create additional inlet drag. Because the F-15 inlet system is not a caret-type inlet with the highly swept edges, it is not employed on current-generation fighter aircraft.
It is therefore desirable to provide a variable inlet which maximizes pressure recovery across the Mach envelope range to obtain higher pressure recovery at the engine face for maximizing thrust and fuel efficiency and to minimize inlet spill drag to maximize the propulsion system net propulsive force, thereby maximizing aircraft performance. It is also desirable that the variable inlet operate in an efficient manner without generating additional complexities such as opening gaps that will require more additional mechanisms or seals for closure.